<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="UTF-8">
  <meta http-equiv="X-UA-Compatible" content="IE=edge">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <title>margin注意事项</title>
  <style>
    .outter{
      background-color: gray;
      width: 400px;
      height: 400px;
      padding: 20px;
    }
    .inner{
      background-color: orange;
      width: 100px;
      height: 100px;
      margin: 20px;
    }
  </style>
</head>
<body>
  <div class="outter">
    <div class="inner"></div>
  </div>
  
</body>
</html>